The present invention is directed to an arrangement for the addition of chlorine dioxide to a water-carrying pipeline.
Water for industrial and commercial may be treated so that it is disinfected thoroughly, and in a safe and an environmentally acceptable manner. Cooling or process waters offer ideal conditions for the multiplication of microorganisms. Slime-forming bacteria in particular form so-called biofilms, which are microbiological contaminations which, in cooling water lines, may severely disrupt heat transfer and cause corrosion.
Because of its activity against microorganisms, chlorine dioxide (ClO2) can be a particularly efficient agent for water disinfection. It is active across a broad pH range and can be used not only to treat industrial waters such as cooling or process waters, in particular, but may also be used—subject to compliance with appropriately low concentration—in the beverage and food industries, in agriculture or in medical technology. A further field of application is in the paper industry, where chlorine dioxide is used to bleach pulp. Lastly, chlorine dioxide also serves for the disinfection of swimming pool water.
The commercial units typical to date for producing chlorine dioxide contain considerable quantities of chlorine dioxide, with all of the attendant risks in the operation of the generating units. The risk is due to the fact that chlorine dioxide is a highly toxic, explosive chemical, which even at low concentrations undergoes explosive decomposition and, in so doing, releases chlorine.
On account of its hazardous nature and low stability, ClO2 is generally not transported or stored. Preferably, the ClO2 is synthesized directly at the site of use, more particularly in the water that is to be treated. In this way, the problem of producing and handling toxic and explosive chlorine dioxide is minimized or eliminated. Accordingly, methods to generate ClO2 in situ and supply it immediately to the water to be treated, without further temporary storage, are conventionally known. Methods for in situ ClO2 generation are described in WO2009/077309, WO2009/077160A1, DE202004005755U1, US2005/0244328A1 and U.S. Pat. No. 4,534,952.
Conventionally, generation of chlorine dioxide (ClO2) in situ is conducted by the chlorite/hydrochloric acid process, in which hydrochloric acid (HCl) is reacted with sodium chlorite (NaClO2) to give ClO2, water (H2O) and sodium chloride (NaCl):5NaClO2+4HCl→4ClO2+5NaCl+2H2O
An advantage of this process is that there are only two reactants to be conveyed into the reactor, namely hydrochloric acid (HCl) and sodium chlorite (NaClO2). Since both chemicals are in aqueous solution, the above technical problems are minimized; however, the corrosiveness of both solutions must be recognized. When mixed in a reactor, the two reactants undergo immediate and vigorous reaction to yield chlorine dioxide (ClO2). The water (H2O) of reaction that is formed, and the water constituents of the reactants supplied in aqueous form, wash the chlorine dioxide in highly concentrated aqueous solution from the reactor, where it becomes diluted with the water to be treated, attaining less hazardous but still biocidal concentrations. A disadvantage of this process is the inevitable formation of sodium chloride (NaCl), which if the solubility limit is exceeded, precipitates in crystalline form and clogs the reactor.
Reactors for the generation of chlorine dioxide in situ within the water to be treated are conventionally arranged within pipelines which carry the water to be treated. In one such arrangement, a reactor having a tubular reaction chamber, is extended essentially along the pipeline with the water to be treated, with the water flowing around the reactor. One example of an axial reactor of this kind is described in DE202004005755O1. Another example is described in DE102010027908A1. With these chlorine dioxide reactors, then, the tubular reaction chamber extends along the pipe and discharges the synthesized chlorine dioxide at the distal end of the reactor through an exit opening which is directed in the longitudinal direction of the pipe, in other words in the flow direction of the water to be treated. With axial pipe reactors of this kind, supplying the reactants is problematic and difficult.
U.S. Pat. No. 4,534,952 describes a pipe reactor for generating chlorine dioxide, which is arranged in a bend in the pipeline with the water to be treated. In the region where the product exits, the reaction chamber extends likewise axially in the flow direction. Since the shaft runs radially, so to speak, at least sectionally, in the region of the bend in the pipe, the supplying of the reactants into the reaction chamber is easier. A disadvantage of this embodiment is that there are sections of the reaction chamber where ambient air, rather than the water to be treated, flows around the reaction chamber, since the two reactants are mixed outside the pipeline. This means that in an accident scenario, toxic chlorine dioxide may be released. A construction of this kind is therefore inadvisable on safety grounds.
German published specification DE1203691 describes a chlorine dioxide synthesis reactor having as a reaction chamber, a dead water zone on the pipeline. Extending into the dead water zone are two open reactant lines via which the reactants are metered into the dead water for the purpose of synthesizing the chlorine dioxide. Within the dead water, the reactants undergo reaction to form chlorine dioxide, which exits from the dead water zone and is entrained by the drinking water to be treated, which flows through the pipeline. However, the arrangement of DE1203691 appears unfavourable from the standpoint of fluid dynamics. Moreover, there is a risk of the base of the dead water zone increasingly salting up. Lastly, the reactant lines run radially, unprotected, through the pipeline.
Therefore, the object of the present invention is to provide an arrangement having high operational reliability, safety and favourable fluid dynamics for the synthesis of chlorine dioxide in situ within a pipeline that carries the water to be treated.